OTP970 Is Required for RNA Editing of Chloroplast ndhB Transcripts in Arabidopsis thaliana

Abstract

RNA editing is essential for compensating for defects or mutations in haploid organelle genomes and is regulated by numerous trans-factors. Pentatricopeptide repeat (PPR) proteins are the prime factors that are involved in RNA editing; however, many have not yet been identified. Here, we screened the plastid-targeted PLS-DYW subfamily of PPR proteins belonging to Arabidopsis thaliana and identified ORGANELLE TRANSCRIPT PROCESSING 970 (OTP970) as a key player in RNA editing in plastids. A loss-of-function otp970 mutant was impaired in RNA editing of ndhB transcripts at site 149 (ndhB-C149). RNA-immunoprecipitation analysis indicated that OTP970 was associated with the ndhB-C149 site. The complementation of the otp970 mutant with OTP970 lacking the DYW domain (OTP970∆DYW) failed to restore the RNA editing of ndhB-C149. ndhB gene encodes the B subunit of the NADH dehydrogenase-like (NDH) complex; however, neither NDH activity and stability nor NDH-PSI supercomplex formation were affected in otp970 mutant compared to the wild type, indicating that alteration in amino acid sequence is not necessary for NdhB function. Together, these results suggest that OTP970 is involved in the RNA editing of ndhB-C149 and that the DYW domain is essential for its function.

The dicot homolog of maize PPR103 carries a C-terminal DYW domain and is required for C-to-U editing of chloroplast RNA transcripts

“…Most DYW PPR proteins have a single editing target and little redundancy between editing factors has been observed, probably due to the specificity with which each protein binds it target RNA (Barkan and Small 2014;Gutmann et al 2020). Indeed, at least six PPR proteins have been identified as required for the Arabidopsis ndhB transcript, with a single site being identified as the target for each protein (Hammani et al 2009;Okuda et al 2009;Okuda et al 2010;Hayes et al 2013;Fu et al 2022;). This contrasts with Arabidopsis QED1 that edits 1 site in each of five Arabidopsis chloroplast transcripts, an usually large number of sites (Wagoner et al 2015).…”